Assessment of light absorbing carbonaceous aerosol and its absorption properties from forest fire in Himalayan...

The study aims to address the optical properties and source of light absorbing carbonaceous aerosols (LAC), during forest fire events at data-deficient Himalayan regions (1800 m a.s.l.) from 2022 to 2024 by using Aethalometer and satellite data. During entire study period equivalent Black Carbon (eBC) mass concentration varied considerably, with an average of 2.45 ± 1.57 μg m^-3 having higher value during summer forest fire, likely due to increased fire intensity, long-range transport, and human activities. The absorption coefficient of eBC and BrC was observed to be 22.2 ± 13.50 M m^-1 at 880 nm and 72.8 ± 70.86 M m^-1 at 370 nm. BrC absorption exhibits greater variability compared to eBC absorption, suggesting that during forest fire events BrC contribution to aerosols absorption is more diverse and dynamic than eBC which more consistent across the events. There is an increasing trend in BrC absorption from 2022 to 2024, coupled with the strong correlation between BrC and eBC absorption (0.85), suggesting as forest fire intensifies, both BrC and eBC emissions increase. The % contribution of BrC absorption at 370 nm to total aerosol light absorption is about 55.1 %. The study addresses the gaps in understanding optical properties of LAC and uncertainties in climate models that tend to underestimate BrC's radiative forcing especially during events like forest fire. Also emphasizes the importance of managing biomass burning to mitigate the impact of atmospheric heating and snowmelt in sensitive Himalayan ecosystems.